1. Field of the Invention
The present invention relates to packaging formed from a thermoplastic polystyrene material and, more particularly, egg cartons formed from a thermoplastic polystyrene material.
2. Description of the Prior Art
Many factors are taken into consideration in the design of egg cartons. Egg protection, aesthetic appearance, print surface area, strength, weight, nestability/denestability, adaptability to accommodate various size eggs, and consistent manufacturing are factors which may be considered to varying degrees in the design of an egg carton. As can be readily appreciated, certain design factors are diametrical, e.g., strength of the carton is typically sacrificed upon reduction in weight and/or thickness, and vice versa.
The importance of many of the design factors can be better appreciated by understanding the "life" of an egg carton. Polystyrene egg cartons are formed and trimmed from a single sheet of polystyrene material to integrally define a lid and a tray. The formed egg cartons are transported, typically by conveyer belt, to a printing machine and imprinted with an egg distributor's trade style, government mandated nutritional information, and retail information, such as UPC labels. The egg cartons are then nested one within another and packaged in bags or pallets for shipping to egg distributors. The volume of the nested egg cartons within each package unit is a direct function of the nestability of the egg cartons. At the egg distributors, through automation, the egg cartons are denested and stamped with necessary information, e.g., expiration dates. Eggs are afterwards packaged into the egg cartons, and the packaged egg cartons are then placed into storage containers ready for shipping to retailers. Various storage containers are used in the industry including cases (each typically holds thirty dozen egg cartons), metal grid baskets (each typically holds fifteen dozen egg cartons), milk crates (each typically holds between twelve dozen and fifteen dozen egg cartons), and racks formed to be wheeled or slid into grocery store display cases (with each rack typically holding between 240-360 dozen egg cartons). Due to the relatively high quantity of egg cartons per storage container, the stored packaged egg cartons can be subjected to relatively high compressive loading. For example, in some of the aforesaid storage containers, the egg cartons are stacked seven high. Taking into consideration that one dozen "jumbo" sized eggs weigh between 30-32 ounces, and assuming seven egg cartons are in a stacked arrangement, with each egg carton containing one dozen "jumbo" sized eggs, the bottom-most egg carton will be subjected to a loading of between 180-192 ounces (11.25-12 pounds) of compressive force. The compressive loading is amplified where the bottom-most egg carton is placed on an irregular surface, such as the bottom of a metal grid basket, wherein greater compressive pressures are applied to the bottom portions of the egg carton contacting the irregular surface (i.e., the compressive loading applied to the bottom-most egg carton is in turn applied to the storage container through a relatively small amount of area, as defined by the portions of the egg carton contacting the storage container, which translates the applied compressive loading to higher pressures being developed in the contacting portions of the egg carton). Once shipped, the egg cartons are displayed at the retail outlet in the respective storage container, or alternatively, stocked on shelving of a display rack or case. Again, significant compressive pressures may be generated upon the packaged egg cartons at display. Finally, the packaged egg cartons are purchased by consumers and taken home for consumption of the eggs.
A commercially successful egg carton is disclosed in U.S. Pat. No. 5,494,164, entitled "EGG CARTON", which issued on Feb. 27, 1996 to the inventor herein. U.S. Pat. No. 5,494,164 discloses an egg carton having cells which are configured to expand toward the interior of the egg carton upon receiving an egg, and having common intersections, each defined by four adjacent cells, which are progressively lowered going outwardly from the center of the tray towards the respective ends of the tray. Although the egg carton of U.S. Pat. No. 5,494,164 has been commercially successful, improvements in egg protection, nesting/denesting and carton strength are always desired.
Another consideration in egg carton design, which is growing in importance, is the temperature control of eggs packaged in the egg carton. Proper refrigeration of eggs combats the spread of Salmonella Enteritidis. As reported in the Wall Street Journal, May 19, 1998, p. B20, col. 5, 4.5 million eggs are annually found to be contaminated with Salmonella Enteriditis, and, since 1985, at least 77 people have died and 26,000 have become ill from the pathogen. The United States Agriculture Department and the United States Food and Drug Administration have proposed requiring shippers to transport eggs and retailers to display eggs at temperatures of 45.degree. F. or below.
It is an object of the subject invention to provide an egg carton with excellent denesting capabilities at reduced stack pitch.
It is an also an object of the subject invention to provide an egg carton having reinforced and stable egg cell bases.
It is yet another object of the subject invention to provide an egg carton having venting features to allow for packaged eggs to properly cool naturally or be cooled artificially.
It is a further object of the subject invention to provide an egg carton formed to accommodate and protect various sized eggs.